class['t]engine_mixin :'t engine_state -> Unixqueue.event_system ->object..end
A useful class fragment that implements state and
request_notification.
method state : 't engine_state
method private set_state : 't engine_state -> unit
method request_notification : (unit -> bool) -> unit
method request_proxy_notification : ('t engine -> bool) -> unit
method private notify : unit -> unit
method event_system : Unixqueue.event_system
